This invention relates to an apparatus and method for making filters for cigarettes. More particularly, this invention relates to an apparatus and method for making filters for cigarettes having a hollow tube embedded therein.
Heretofore, filter making machines have been known in which hollow tubes, for example of plastic, are inserted into a moving stream of fibrous filter material such as cellulose acetate (tow). In some cases, the hollow tube has been continuous with the tow such that the filters subsequently cut from resulting filter rods have a tube extending from end to end. In other cases, where a filter is to be made with a hollow tube extending only partially within the filter, machines have been known for inserting short hollow tubes into a moving stream of tow at spaced intervals. In these latter machines, the moving tube-containing stream must be cut through a tube containing section so as to sever the tube in half. If the tube is not severed in half, a short tube portion will be incorporated in one resultant filter and a long tube portion will be incorporated in a second resultant filter. In either case, the efficiency of the filter can be impaired. Also, if the tube portion becomes too long, the result may be a filter with a tube extending from end to end.
In order to overcome the problems associated with machines in which hollow tubes are inserted into a moving stream of tow, it has been known to provide the mechanism for inserting the tubes with a transmission which can be manually adjusted to advance or retard the point at which a tube is inserted into the two. However, since the filter making machine usually operates at high speed and since the detection of an improper placement of the tubes usually occurs after cutting of the filter rod, a large number of improperly made filters may be produced before an adjustment can be made.
Accordingly, it is an object of the invention to provide an apparatus and method for automatically sensing and correcting the position of hollow tubes inside a stream of tow.
It is another object of the invention to sense the position of hollow tubes in a stream of tow before the stream is cut into filter rods.
It is another object of the invention to detect an incorrect positioning of hollow tubes in a moving stream of tow and to automatically correct the position of subsequently inserted tubes in the tow stream.
It is another object of the invention to reduce the number of improperly made tube-containing filters in automatic machinery.
Briefly, the invention provides an apparatus for incorporation into a machine for making filter rods having tube-containing sections which is capable of sensing the position of the tubes and correcting the position of subsequently positioned tubes. The machine includes means for supplying a travelling stream of fibrous filter material (tow), means for inserting hollow tubes into the fibrous filter material and a knife for cutting the stream of hollow tube-containing fibrous filter material into filter rods. The sensing and correction apparatus includes a sensing means upstream of the knife for sensing the presence of a hollow tube in the stream of tow and for generating a position signal in response thereto and means for generating a constant reference signal in response to the knife cutting the stream. In addition, the apparatus has a comparison means for comparing the position signal with the reference signal and for generating a correction signal in response to a disparity between the position signal and reference signal. Also, the apparatus has a correction means for receiving the correction signal, if any, which correction means is connected to the tube inserting means of the machine so as to adjust the tube inserting means to correct the position at which a tube is inserted into the tow stream.
The sensing means can be in the form of a density gauge of known construction for measuring the density of the tube-containing stream over a period of time and for generating the position signal corresponding to this measurement. The means for generating the reference signal is actuated by the knife of the machine to emit the reference signal as a cut is made. If the position signal exceeds the value of the reference signal, the timing assembly advances the inserting means to insert subsequent tubes into the tow stream at an earlier time. If the position signal is less than the value of the reference signal, the timing assembly retards the inserting means to insert the tubes at a later time.
The position signal and reference signal may be of any suitable type. For example, each may represent a value which can be compared algebraically. Also, the signals may be compared with respect to time. In this case, the duration of the position signal relative to the duration of the reference signal may be compared. If the position signal is longer, then the inserting means is advanced and if shorter, the inserting means is retarded.
As the position signal is generated earlier than the reference signal, a time delay is built into the comparison means so that the two signals for a given filter rod can be compared.
The invention also provides a method to sense the position of hollow tubes within a moving stream of tow. The method comprises the steps of sensing the position of the tube within the tow and generating a position signal in response thereto; generating a reference signal indicative of the cutting of a filter rod from the stream; comparing the position signal to the reference signal and generating a correction signal in response to a disparity therebetween; and correcting the position of a hollow tube subsequently inserted in the tow in response to the correction signal.